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   <title>KDbg - User's Manual - Type Tables</title>
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<p><a href="index.html">Contents</a></p>
<h1>
KDbg's Type Table</h1>
<p>KDbg can display the contents of single members of structured types, so
that it is not necessary to expand the variable in the <a href="localvars.html">local
variables window</a> or <a href="watches.html">watched expressions window</a>.
The information which member variable is displayed is stored in <em>type
tables</em>. There is generally one type table per shared library.</p>
<p>KDbg's type tables are located under <tt>$prefix/share/apps/kdbg/types</tt>.
The file names end with <tt>.kdbgtt</tt>. Example: The type table for <tt>libqt.so</tt>
is named <tt>qt.kdbgtt</tt>.</p>
<p>A type table file obeys the regular KDE configuration file syntax. The
file has the following groups:</p>
<ul>
<li>
A group <tt>[Type Table]</tt> which lists the types and information how
the debugger can identify whether the program is linked against the library.</li>

<li>
A group for each type which has information about how the value of such
a type is displayed by KDbg.</li>
</ul>
<p>In order to determine which type tables apply to the program being debugged
KDbg lists the shared libraries it is linked to. Then it matches the names
against the <tt>ShlibRE</tt> entries of all type tables. Those that match
are used. If a type appears in several type tables, it is unspecified which
one will be used.</p>
<p>KDbg's type recognition only works for libraries that are linked dynamically
to the program being debugged.</p>
<h2>
The <tt>[Type Table]</tt> group</h2>
<p>This group contains the following entries:</p>
<ul>
<li>
<tt>Types1</tt>, <tt>Types2</tt>, etc. These entries name the types. Each
of them is a comma-separated list of type names. Each of the entries can
list any number of types. (The types names can be distributed to several
lines just so that the lines don't get excessivly long.) No blank space
is allowed in these lines. The entries must be numbered consecutively (KDbg
stops reading at the first gap), although an entry may be empty (i.e. contain
no type at all). Sometimes the order in which the names are listed is important
(see <tt>Alias</tt> types below).</li>

<li>
<tt>ShlibRE</tt>. KDbg uses this entry to determine if the type table applies
to the program being debugged. For this purpose KDbg determines the shared
libraries to which the program is linked. If any of the libraries matches
this entry, the type table applies. The regular expression is a Qt-regular
expression (the metacharacters <tt>.*?[]^$\</tt> are recognized in the
usual way, but there is no possibility to group characters.)</li>

<li>
<tt>LibDisplayName</tt>. This entry is used in lists where the available
type tables are listed to identify this type table.

<br><font size=-1>This is not used currently.</font></li>

<li>
<tt>EnableBuiltin</tt> lists extensions that must be enabled if this
library is used. Currently, two builtins are supported:
<ul>
<li>
<tt>QString::Data</tt> is used to display unicode strings of Qt's <tt>QString</tt>
class. See below.</li>
<li><tt>QCharIsShort</tt> is used only in connection with <tt>QString::Data</tt>
to specify that a unicode character is stored in an object of type <tt>short</tt>.
See <tt>qt3.kdbgtt</tt> for examples.</li></ul></li>
</ul>

<h2>
The type's group</h2>
<p>There is one group for each type that is named exactly as the type. <font size=-1>At
the moment C++ template classes are not supported.</font> Each group contains
the following entries:</p>
<ul>
<li>
<tt>Display</tt> determines how the value of the type is displayed by KDbg.
The string must contain 1 to 5 percent characters '<tt>%</tt>'. These are
replaced by the results of the expressions printed by the <tt>Expr</tt><i>x</i>
entries.</li>

<li>
One or more of <tt>Expr1</tt>, <tt>Expr2</tt>, etc. Each of them must contain
<b>exactly
one</b> <tt>%s</tt> sequence, which will be replaced by the expression
whose value is investigate. The so constructed expression is submitted
to gdb, and the result substituted back for the corresponding percent character
in the <tt>Display</tt> string.</li>

<li>
<tt>Alias</tt> names an alias type. If this entry is present, the type
is treated like the specified type. That alias type must appear before
this type in the <tt>Types</tt><i>x</i> entries in the <tt>Type Table</tt>.</li>
</ul>
<p><font size=-1>Currently the number of expressions per type is limited to
5. This can easily be changed if it's too restrictive, but I recommend
not to go to that limit at all - it will slow down the debugging process.</font></p>
<p>KDbg recognizes a special extension that is used to display Qt 2.x's and Qt 3.x's
unicode strings: If an <tt>Expr</tt><i>x</i> is prepended with <tt>/QString::Data</tt>,
it is assumed that the result of the expression is a pointer to a <tt>QString::Data</tt>.
The value displayed is the unicode string that this instance of <tt>QString::Data</tt>
represents (which can be <tt>QString::null</tt> if it is Qt's well-defined
null string or <tt>(null)</tt> if the <tt>unicode</tt> member is the null
pointer). See <tt>qt2.kdbgtt</tt> for examples.</p>
<p>Tip: It is not necessary to define derived types if they ought to be
treated the same as the base class - KDbg can deduce derived types and
uses the type specification of the (leftmost) base class. You can use the
<tt>Alias</tt>
entry to quickly specify that a type should be treated like a non-leftmost
base class for a multiple-inheritance class.</p>
<h2>
An example</h2>
<p>The example shows how <tt>QString</tt> and <tt>QObject</tt> are defined
in <tt>qt.kdbgtt</tt>. Additionally, <tt>QTableView</tt> is defined as
an alias of <tt>QObject</tt>. This example applies to Qt 1.x, which is
located in shared library whose name ends in <tt>libqt.so.1</tt>.</p>
<pre>[Type Table]
Types1=QString
Types2=QObject,QTableView
LibDisplayName=libqt 1.x
ShlibRE=libqt\.so\.1$
[QString]
Display={ % }
Expr1=(%s).shd->data
[QObject]
Display={ name=% #chld=% }
Expr1=(%s).objname
Expr2=(%s).childObjects->numNodes
[QTableView]
Alias=QObject</pre>
<p>Note that it is safer to wrap the <tt>%s</tt> in parentheses.</p>
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